1. Field of the Invention
This invention relates to power supplies and in particular relates to small form factor power supplies.
2. Background of the Invention
Prior art power supplies include a variety of techniques, particularly those used for powering microelectronics such as the class of computers commonly known as "notebook" computers such as the Powerbook Series available from Apple Computer of Cupertino Calif. and the Thinkpad Series available from International Business Machines of Armonk, N.Y. More recently, even smaller personal computers referred to as "sub-notebooks" have also been developed by various companies such as Hewlett-Packard's Omnibook. The goal of these notebooks and sub-notebooks designs is to reduce the size and weight of the product. Currently, notebooks typically weigh about six pounds and sub-notebooks weigh slightly less than four pounds.
Many of these notebook and sub-notebook computers have a battery that must be recharged. Also, typically the computers are designed to be operated from external power sources such as line current and the electrical power system of automobiles.
To power these computers, the manufacturer typically provides an external power source. The external power source may be a switching power supply that may weigh close to a pound and may be about eight inches long, four inches wide and about four inches high. Smaller power supplies do exist but frequently they lack sufficient power to charge new batteries such as nickel hydride batteries.
Such external power supplies therefore contribute substantial additional weight that the user of the computer must carry with him or her to permit battery charging and/or operation from an electrical socket. Further, the external power supply is bulky and may not be readily carried in typical cases for such notebook and sub-notebook computers. In addition, conventional power supplies often have difficulty providing the necessary power curve to recharge batteries that have been thoroughly discharged.
While it has long been known to be desirable to reduce the size and weight: of the power supply, this has not been readily accomplished. Many of the components such as the transformer core are bulky and have significant weight. Further, such power supplies may need to be able to provide DC power of up to seventy-five watts, thereby generating substantial heat. Due to the inherent inefficiencies of power supplies, this results in substantial heat being generated within the power supply. Reduction of the volume, weight and heat are all critical considerations for a power supply in this type of application and cannot be readily accomplished. In particular, it is believed to be desirable to have a package as thin as possible and designed to fit within a standard pocket on a shirt or a standard calculator pocket on a brief case.